WO2016119500A1 - Steel plate having high crack-arresting performance, and manufacturing method thereof - Google Patents

Abstract

A steel plate having a high crack-arresting performance, and manufacturing method thereof; contents (by wt.%) of chemical elements in the steel plate are as follow: 0.04% ≤ C ≤ 0.12%, 0.10% ≤ Si ≤ 0.30%, 0.60% ≤ Mn ≤ 1.90%, P ≤ 0.015%, S ≤ 0.0040%, 0.01% ≤ Cr ≤ 0.40%, 0.10% ≤ Ni ≤ 0.70%, 0.001% ≤ Mo ≤ 0.40%, 0.001% ≤ Cu ≤ 0.50%, 0.01% ≤ Al ≤ 0.06%, 0.01% ≤ Nb ≤ 0.06%, 0.01% ≤ Ti ≤ 0.06%, N ≤ 0.007%, 0.0001% ≤ Ca ≤ 0.0045%, and 1.0 ≤ Ca/S ≤ 2.0, and the balances are Fe and other unavoidable impurities. Also provided is a manufacturing method of the steel plate, the manufacturing method comprising the following steps: smelting, external refining, casting, slab heating, controlled rolling and controlled cooling.

Description

Steel plate with high crack arresting property and manufacturing method thereof Technical field

The present invention relates to a steel sheet and a method of manufacturing the same, and more particularly to an alloy steel sheet and a method of manufacturing the same.

Background technique

In recent years, awareness of the safety of ships and offshore structures and environmental protection problems due to safety is gradually increasing. For large welded structures, such as welded structures in ships and offshore structures, these welded structures inevitably crack in the event of an accident, especially during an accident, due to the presence of cracks and local brittleness in these structures. Zones, or due to the geometric stress concentration of the structure, with welding residual stress, crack initiation can occur in these structures. Due to the large number of welded structures in ships and offshore structures, it is impossible to perform 100% flaw detection in such engineering structures. At this time, it is necessary to consider the premature fatigue in the engineering structure. crack. For thick plates, the brittle cracks generated at the welds are usually propagated along the welds without deflection. Even if the cracks enter the base metal, it is difficult to stop, and the plastic deformation also reduces the steel. Cracking ability. It can be seen that although the crack initiation toughness is very important for the weld and the heat affected zone of the weld, it is more important that the base material can stop the crack which is rapidly expanding from the weld crack, that is, the crack arrest toughness is also used to improve the safety of the steel plate. One of the important indicators of sex.

In order to improve the safety and reliability of engineering structures such as ships and oceans, in order to avoid structural fracture accidents caused by brittle fracture of steel plates, it is necessary to improve the crack arrest performance of steel plates under the premise of ensuring the fracture toughness of the structure. .

Japanese Patent Publication No. CN101307412A, published on November 19, 2008, entitled "Stainless steel crack propagation stop characteristic and steel sheet having excellent toughness at the center portion of the thickness" and a method for producing the same, discloses a steel sheet. The mass percentage (wt.%) of each chemical element in the steel sheet is: C: 0.01-0.06, Si: 0.01-0.8, Mn: 1.0-1.8, Cr: 0.05-0.5, Ni: 0.20-0.8, Mo : 0.05-0.5, Cu: 0.05-0.08, Alt: 0.01-0.08, Nb: 0.02-0.08, Ti: 0.005-0.03, B: 0.00003-0.0003, Ca: 0.0005-0.0030, N: 0.003-0.008, REM: 0.0050 -0.030; and the steel sheet is composed of a ferrite-based structure, and the orientation of the two crystals is in the region of the entire thickness of the portion of the outermost layer of the steel sheet corresponding to the thickness of 1%. Large angle grain boundary with a difference of 15° or more The crystal grains enclosed have an average equivalent circle diameter of 8 mm or less and satisfy the relationship of the following formula (1): 1-(A2 - A1) / 100 ≥ 0.8, wherein A1: crystal grains having a crystal orientation difference of 55 or more The proportion (area%) in the population, A2: the proportion (area%) of the crystal grains having a crystal orientation difference of less than 15° in the whole.

Japanese Laid-Open Patent Publication No. JP 04-141517A, the entire disclosure of which is incorporated herein by reference. The mass percentage (wt.%) of each chemical element of the steel sheet is: C: 0.01-0.30, Si: ≤ 0.5, Mn: ≤ 2.0, Cr: ≤ 0.5, Ni: ≤ 1.0, Mo: ≤ 0.5, Cu : ≤ 0.9, V: ≤ 0.1, Alt: 0.001-0.1, Nb: 0.005-0.05, Ti: 0.005-0.02, B: 0.0003-0.003, Ca: 0.0003-0.005, N: 0.001-0.008, Mg: 0.0003-0.005 ;REM: 0.0003-0.005; the balance is Fe and other unavoidable impurities. The technical solution of the above patent document adopts ultra-low carbon and repeated phase change means to obtain surface ultrafine crystal.

Japanese Patent Publication No. JP2002-241891A, published on August 28, 2002, entitled "Structural steel having excellent brittle crack propagation stop characteristics and fatigue crack propagation characteristics after plastic deformation, and a method for producing the same" A steel plate having a mass percentage (wt.%) of each chemical element: C: ≤ 0.03, Si: ≤ 0.5, Mn: 1.0-2.0, Cr: ≤ 0.5, Ni: ≤ 2.0, Mo: ≤ 0.5, Cu: 0.7-2.0, V: 0.005-0.2, Nb: 0.005-0.20, Ti: 0.005-0.20, B: 0.0003-0.005, Ca: 0.0005-0.003, N: 0.003-0.008, REM: 0.0050-0.030; The balance is Fe and other unavoidable impurities. The steel plate in the Japanese patent document adopts a chemical element composition design of ultra-low carbon, high Ni and no Al, and through the controlled rolling process, the (211) surface texture parallel to the rolling plane is developed, and (100) The crystal texture is weakened.

Summary of the invention

The object of the present invention is to provide a steel sheet having high crack arresting property, which has high strength and good low temperature impact toughness, and has a yield strength of ≥400 MPa, and a -40 °C Charpy V-notch impact energy ≥64 J. In addition, compared with the steel plate in the prior art, it has excellent crack arresting performance, and its non-plastic transition temperature (NDTT, Nil-Ductility Transition Temperature) ≤ -70 ° C, which is particularly suitable for use in ships, offshore engineering structures, etc. Manufacturing field.

In order to achieve the above object, the present invention proposes a steel sheet having high crack arresting property, wherein the chemical element mass percentage content is:

0.04% ≤ C ≤ 0.12%;

0.10% ≤ Si ≤ 0.30%;

0.60% ≤ Mn ≤ 1.90%;

P≤0.015%;

S≤0.0040%;

0.01% ≤ Cr ≤ 0.40%;

0.10% ≤ Ni ≤ 0.70%;

0.001% ≤ Mo ≤ 0.40%;

0.001% ≤ Cu ≤ 0.50%;

0.01% ≤ Al ≤ 0.06%;

0.01% ≤ Nb ≤ 0.06%;

0.01% ≤ Ti ≤ 0.06%;

N ≤ 0.007%;

0.0001% ≤ Ca ≤ 0.0045%; and 1.0 ≤ Ca / S ≤ 2.0;

The balance is Fe and other unavoidable impurities.

The design principles of each chemical element in the technical solution are as follows:

Carbon: C is the most basic strengthening element. When C is dissolved in steel, a gap solid solution can be formed to function as a solid solution strengthening, and C can also be combined with a forming element of a strong carbide to form a carbide precipitate, thereby functioning as a precipitation strengthening. At the same time, C can also improve the hardenability of steel. However, for this technical solution, C which is too high in content will adversely affect the ductility, toughness, crack arrestability and weldability of the steel sheet, and also reduce the solid solution of microalloying elements such as Nb and V. Affect the precipitation enhancement effect. In view of this, the content of the C element in the steel sheet having high crack arresting property according to the present invention is controlled to be between 0.04 and 0.12%.

Silicon: Si acts as a reducing agent and a deoxidizer to eliminate the adverse effects of FeO inclusions on steel. Si exists in a solid solution state in ferrite or austenite, which can increase the hardness and strength of ferrite or austenite and reduce the austenite phase region. However, as the silicon content increases, the weldability of the steel is lowered. Therefore, the present invention controls Si to 0.10% ≤ Si ≤ 0.30%.

Manganese: Mn is one of the most basic alloying elements for low-alloy high-strength steels. The strength of the steel sheet is increased by solid solution strengthening of Mn to compensate for the loss of strength of the steel sheet due to a decrease in the C content in the steel sheet. Mn is also an element that expands the γ phase region, which can reduce the γ→α phase temperature of steel. Degree, help to obtain fine phase change products in the steel plate to improve the toughness and crack arrest performance of the steel plate. However, when the Mn content is too high, segregation tends to occur at the center position of the steel sheet for the extra-thick steel sheet, thereby lowering the low-temperature toughness at the center portion of the steel sheet. Therefore, the mass percentage of Mn in the steel sheet having high crack arresting property of the present invention is from 0.60 to 1.90%.

Chromium: Cr is one of the important elements for improving the hardenability of steel sheets. For steel plates with extra-thickness specifications, it is necessary to increase the hardenability of the steel sheet by adding more Cr elements to compensate for the strength loss caused by the thickness, and to improve the strength of the steel sheet while improving the performance of the steel sheet in the thickness direction. Uniformity. Cr can also inhibit the transformation of pro-eutectoid ferrite and pearlite, which is beneficial to obtain acicular ferrite structure. Once too much Cr and Mn are added to the steel sheet at the same time, it will lead to the formation of a low-melting Cr-Mn composite oxide, which will cause the surface of the steel sheet to form surface cracks during hot working, and will seriously deteriorate the weldability of the steel sheet. . For this reason, the content of Cr in the technical solution of the present invention should be limited to a range of 0.01% to 0.40%.

Nickel: Ni is an element that improves the low temperature toughness of materials. Adding an appropriate amount of Ni can reduce the stacking fault energy of the crystal, facilitate the slip motion of the dislocation, improve the impact toughness of the material, and especially improve the impact toughness of the central portion of the extra-thick plate. At the same time, the addition of Ni element in the technical solution can also improve the crack arrest performance of the steel sheet. In addition, Ni can also enhance the hardenability of Mo. However, if the Ni content is too high, the slab surface tends to form a high-viscosity iron oxide scale, which is difficult to remove in the subsequent manufacturing process, thereby affecting the surface quality and fatigue properties of the steel sheet. In addition, when the Ni content is too high, it is disadvantageous for the welding performance of the extra-thick steel plate. In view of this, the Ni content in the steel sheet having high crack arresting property according to the present invention needs to be controlled to be 0.10% to 0.70%.

Molybdenum: Mo is an element that improves the hardenability of a steel sheet, and its effect is second only to the Mn element. Mo can not only effectively increase the strength of the steel sheet, but also inhibit the transformation of the pro-eutectoid ferrite and pearlite to help the steel sheet obtain the acicular ferrite structure. However, as the Mo content increases, the yield strength of the steel sheet gradually increases, while the plasticity of the steel sheet gradually decreases. For the steel sheet having high crack arresting property of the present invention, the mass percentage content of Mo should be set to 0.001% to 0.40%.

Copper: Cu can appropriately improve the hardenability of the steel sheet, and Cu can also improve the atmospheric corrosion resistance of the steel sheet. However, the addition of an excessively high amount of Cu element to the steel deteriorates the weldability of the steel sheet, so the content of the Cu element in the steel sheet having high crack arresting property according to the present invention is controlled to be 0.001% to 0.50%.

Aluminum: Al is an element added to steel for deoxidation. After the deoxidation is complete, Al lowers the steel plate The content of O in the steel to improve the aging properties of the steel sheet. In addition, the addition of an appropriate amount of Al is also advantageous for refining the grains, thereby improving the toughness of the steel. Therefore, the content of the Al element in the steel sheet having high crack arresting property in the present invention is limited to 0.01 to 0.06%.

铌: In microalloyed steels, Nb is one of the most effective elements for increasing the recrystallization termination temperature. Nb can effectively reduce the rolling mill load and has a significant effect on grain refinement. In the steel sheet according to the present invention, the rolling deformation is completed in the recrystallization and non-recrystallization rolling stages, and at this stage, Nb is precipitated by strain to inhibit the recovery and recrystallization of the deformed austenite, thereby refining The effect of grain size. However, due to the limitation of the C content and the influence of the heating temperature, the Nb having a too high content cannot be dissolved, and the Nb is not advantageous. At the same time, Nb is also an expensive metal element, and adding more Nb will increase the manufacturing cost accordingly. Therefore, the Nb content in the steel sheet having high crack arresting property of the present invention should be controlled to be 0.01% to 0.06%.

Titanium: Ti is a strong solid N element. Since the Ti/N ratio is 3.42, a certain amount of N element can be fixed by using a small amount of Ti. For example, Ti of about 0.02 wt.% can fix N in a steel having a mass percentage of 60 ppm or less. In the slab continuous casting, the added Ti can form a fine high-temperature stable TiN precipitation phase with N. Such fine TiN particles can effectively hinder the growth of austenite grains during reheating of the slab, and contribute to the improvement of the solid solubility of Nb in austenite. For extra-thick steel plates, the addition of an appropriate Ti content is advantageous for the formation of stable TiN particles, which acts to suppress grain growth in the heat-affected zone during welding to improve the impact toughness of the weld heat affected zone. According to the technical solution of the present invention, it is necessary to limit the Ti content in the steel sheet to be in the range of 0.01% to 0.06%.

Nitrogen: The nitride formed by N and alloying elements is a non-metallic inclusion, and more importantly, the N element reduces the role of the alloying element. However, N also has a beneficial effect, and TiN formed with Ti can prevent the growth of austenite grains when the slab is heated. However, in general, its side effects are greater, so the technical solution limits the N content to ≤0.007%.

Calcium: The form of sulfide can be controlled by Ca treatment, the anisotropy of the steel sheet can be improved, and the low temperature toughness of the steel sheet can be improved. When the Ca content is less than 0.0001 wt.%, it does not produce any effect, and when the Ca content is more than 0.0045.wt%, many CaO, CaS are generated, and large inclusions are formed, which damages the toughness of the steel sheet. It even affects the welding performance of the steel sheet. Therefore, in the steel sheet having high crack arresting property of the present invention, it is necessary to set the Ca content to 0.0001% to 0.0045%.

Phosphorus, sulfur: P and S are inevitable harmful impurity elements in steel, they are easily formed in steel Defects such as segregation and inclusions deteriorate the weldability, impact toughness and anti-HIC performance of the steel sheet. For this reason, it is necessary to control P ≤ 0.015 wt.% in the steel sheet having high crack arresting property of the present invention, and to control S to ≤ 0.0040 wt.%. For the S element, the inclusion treatment of the S can be spheroidized and evenly distributed by the Ca treatment inclusion modification technique, reducing the influence on the toughness and corrosivity of the steel sheet. Ca and S also need to satisfy: 1.0 ≤ Ca / S ≤ 2.0 in order to obtain a good sulfide treatment effect, thereby improving the crack arrest performance of the steel sheet.

Compared with the steel plate in the prior art, the steel plate with high crack arresting property of the present invention does not add alloying elements such as V, Zr and W, and adopts low C, Ni-Cr-Mo alloying and Nb, Ti micro. Alloyed component system.

Further, the steel sheet having high crack arresting property of the present invention has an average effective crystal grain size d ≤ 7 μm and a grain orientation difference of ≥ 15°.

For the present technical solution, the inventors have found that a small angle grain boundary (grain orientation difference < 15°) does not effectively prevent crack propagation and thus has no effect on the toughness of the steel. This is because, in the small angle region, the grain boundary energy E increases with orientation, and when the orientation difference is ≥15°, the grain boundary can reach the maximum value and remains unchanged. Only at large angle grain boundaries where the grain orientation difference is ≥15°, the cleavage crack can undergo a significant transition, which consumes more energy. Therefore, the structural unit with a grain orientation difference of ≥15° can be used as an effective crystal grain for controlling the cleavage crack propagation, and the higher the ratio of the large-angle grain boundary, the better the crack growth resistance is prevented. Therefore, the smaller the effective grain size obtained, the stronger the ability to prevent crack propagation, that is, the better the crack arrest performance. Further, the inventors of the present technical solution have found that when the average effective grain size d ≤ 7 μm, the crack arresting property is excellent, and conversely, the crack arresting property is rapidly lowered.

The steel material consists of a myriad of crystal grains. During the phase transformation, the growth direction may be different, that is, the grain orientation is different (substructures with uniform grain orientation form a grain), different crystals The difference in orientation between the particles is the difference in grain orientation. This difference in orientation is determined by setting a coordinate system. After determining the orientation of different crystal grains, the difference can be calculated. The general grain orientation difference can be directly measured by EBSD and other methods. This technical terminology is well known to those skilled in the art, and thus is only briefly described herein and will not be described again.

The average effective grain size of the above-mentioned steel sheet having high crack arrestability needs to be obtained mainly by rational composition design and subsequent process control.

Further, the above average effective crystal grain size d=10-Ceq-d _A /20-2R-(Tn-Ar3)/70-(Tn-T _E )/500-CR/20-F _A /5; Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15, the unit is wt.%; d _A represents the original austenite grain size, the unit is μm; R represents rolling The cumulative reduction rate in the process is in %; Tn is the cooling temperature in °C; Ar3 is the starting phase transition temperature of the steel during slow cooling, the unit is °C; T _E is the final cooling temperature, the unit is °C CR represents the cooling rate in °C/s; F _A represents the comparative example of acicular ferrite.

It should be noted that the present technical solution does not contain the V element, and therefore, in the above carbon equivalent formula, the content of the V element is always zero.

Further, the steel sheet having high crack arresting property according to the present invention further contains B, which satisfies: 0 < B ≤ 0.0025 wt.%.

The B element mainly serves to improve the hardenability of the steel sheet to ensure the mechanical properties of the steel sheet. When the B content is less than 0.0025 wt.%, the effect that can be achieved is optimal. The premise that B can function is that it must be dissolved in steel, and the addition of Mo and Ti contributes to the improvement of the hardenability of B. At the same time, too high a C content will lower the hardenability of B, and based on this, in the case where B is added, the content of C should be kept at a low level. In order to further obtain a better hardenability effect, it is necessary to add B in the steel sheet having high crack arresting property of the patent, and control the content thereof to be: 0 < B ≤ 0.0025%.

Further, in the steel sheet having high crack arresting property according to the present invention, C and Mn also satisfy: 0.10 wt% ≤ C + Mn / 6 ≤ 0.50 wt%.

Further, in the steel sheet having high crack arresting property according to the present invention, Cr, Mo, B, C and Mn also satisfy: 0.9 wt% ≤ (Cr + Mo + B) / (C + Mn / 6) ≤ 3.3 wt%.

Further, in the steel sheet having high crack arresting property according to the present invention, Ni, Nb, Ti, Al, C and Mn also satisfy: 0.9 wt% ≤ (Ni + Nb + Ti + Al) / (C + Mn /6) ≤ 2.2 wt%.

The above-mentioned added alloying elements are controlled under the premise of the defined mass percentage content, and further defining that these elements satisfy the above relationship is to ensure the balance of the alloying element content, so as to further ensure that the steel sheet obtains good strength and toughness matching, thereby The steel plate provides better crack arrest performance.

Further, the microstructure of the steel sheet having high crack arresting property according to the present invention is acicular ferrite + polygonal ferrite.

In the technical solution, the microstructure is defined as ferrite + acicular ferrite, on the one hand, because the acicular ferrite itself has good crack arresting property, and on the other hand, because the two-phase structure has a lower The yield ratio is sufficient to absorb energy and improve the crack arrest performance.

Further, the comparative example (area ratio) of the above acicular ferrite is ≥90%.

The technical solution defines that acicular ferrite ≥90% is beneficial to further prevent crack propagation and improve the crack arrest performance of the steel.

Accordingly, the present invention also provides the above-described method for producing a steel sheet having high crack arresting properties, which comprises the steps of: smelting, refining, casting, slab heating, controlled rolling, and controlled cooling.

Further, in the method for producing a steel sheet having high crack arresting property according to the present invention, in the controlled rolling step, reheating is performed before the rolling, and the heating temperature T is =1120+420 C _Nb +190 C _Ti ±20, wherein the temperature unit is °C, C _Nb is the content of Nb, the unit is wt.%, and C _Ti is the content of Ti, and the unit is wt.%.

The purpose of setting the reheating temperature of the steel sheet slab is to ensure sufficient solid solution of microalloying elements such as Nb, V, Ti, etc., and to ensure precipitation of carbonitrides in the subsequent rolling process to prevent recrystallized grains. Growing up, thus playing the role of refining the grains.

Further, in the method for producing a steel sheet having high crack arresting property according to the present invention, in the controlled rolling step, the rolling temperature is Ar3+200°C to Ar3+350°C, and the finishing rolling temperature is Ar3+40°C. ~ Ar3 + 100 ° C.

Among them, Ar3 is the temperature at which the austenite changes to a ferrite equilibrium phase transition, and the arc rolling temperature is controlled to Ar3+200°C to Ar3+350°C in order to ensure that the steel sheet starts rolling in the recrystallization zone to fully recrystallize. To refine the grain, and to control the finishing temperature to Ar3+40°C～Ar3+100°C, in order to obtain the deformation of the steel plate in the austenite region to increase the deformation point, thereby increasing the nucleation point and promoting the carbon. The precipitation of the nitride further effects the precipitation precipitation strengthening.

Further, in the method for producing a steel sheet having high crack arresting property according to the present invention, the cumulative reduction ratio is 60 to 99% in the controlled rolling step.

The cumulative reduction ratio in the controlled rolling step is limited to 60 to 99% in order to sufficiently deform the steel sheet, to refine the grain in the steel, and in particular to ensure sufficient deformation of the core portion of the steel sheet to obtain a uniform structure.

Further, in the method for producing a steel sheet having high crack arresting property according to the present invention, in the controlled cooling step, the cooling temperature is Ar3 + 15 ° C to Ar 3 + 50 ° C, and the final cooling temperature is 250 to 450 ° C. .

In the above technical solution, the reason for setting the cooling temperature is to rapidly cool the steel sheet under the condition of complete austenitizing to obtain the microstructure required for the steel sheet, and the reason for setting the final cooling temperature is as follows: The final cooling temperature range is lower than the phase transition end temperature of the acicular ferrite, which can cause the steel sheet to undergo a sufficient phase transformation, thereby obtaining more than 90% of acicular ferrite, thereby giving the steel sheet good strength and crack arresting performance. .

Further, in the method for producing a steel sheet having high crack arresting property according to the present invention, in the controlled cooling step, the cooling rate is 10 to 30 ° C/s.

In the above controlled cooling step, in order to avoid the precipitation of pro-eutectoid ferrite and pearlite in the steel, in order to obtain more acicular ferrite structure, to ensure that the steel plate has good crack arresting performance, the cooling rate is obtained. The control is 10 to 30 ° C / s.

The steel plate with high crack arresting property of the invention has high strength and good low temperature impact toughness, and its yield strength is ≥400Mpa, and the -40°C Charpy V-notch impact energy is ≥64J.

Further, the steel sheet having high crack arresting property according to the present invention has excellent crack arresting performance and has a plasticity-free transition temperature (NDTT) ≤ -70 ° C as compared with the steel sheet of the same thickness in the prior art.

In addition, the technical solution described in the present invention is capable of producing a steel sheet having a high crack arresting property of thickness ≤ 90 mm, and is particularly suitable for production in the field of marine and offshore engineering structures.

detailed description

The steel sheet having high crack arresting property and the manufacturing method thereof according to the present invention will be further explained and explained below with reference to specific embodiments. However, the explanation and description are not intended to unduly limit the technical solutions of the present invention.

The steel sheets in Examples A1 to A8 were produced in accordance with the following procedures:

1) smelting;

2) Furnace refining: The mass percentage of each chemical element in the steel sheets of the control examples A1 to A8 is as shown in Tables 1 and 3;

3) casting;

4) slab heating;

5) Controlled rolling: reheating before opening and rolling, and heating temperature T is =1120+420C _Nb +190C _Ti ±20, wherein the temperature unit is °C, and C _Nb is Nb content, the unit is wt.% , C _Ti is the content of Ti, the unit is wt.%, the rolling temperature is Ar3+200°C～Ar3+350°C, and the finishing rolling temperature is Ar3+40°C～Ar3+100°C, which is accumulated during the rolling process. The reduction rate is 60 to 99%;

6) controlled cooling: the opening temperature is Ar3 + 15 ° C ~ Ar3 + 50 ° C, the final cooling temperature is 250 ~ 450 ° C, the cooling rate is 10 ~ 30 ° C / s;

7) Finally, a steel sheet having high crack arresting property is obtained, and the average effective grain size of the steel sheet is d=10Ceq-d _A /20-2R-(Tn-Ar3)/70-(Tn-T _E )/500- CR/20-F _A /5; wherein Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15, the unit is wt.%; d _A represents the original austenite crystal Particle size, the unit is μm; R represents the cumulative reduction rate during rolling, the unit is %; Tn represents the cooling temperature, the unit is °C; Ar3 represents the initial phase transition temperature of the steel during slow cooling, the unit is °C; T _E represents the final cooling temperature in ° C; CR represents the cooling rate in ° C / s; F _A represents the acicular ferrite comparison example, and the microstructure of the steel plate is acicular ferrite + polygonal ferrite Among them, the comparative example (area ratio) of acicular ferrite is ≥90%.

The specific process parameters in each step involved in the above manufacturing method are detailed in Table 2.

Table 1 lists the mass percentage contents of the respective chemical elements in the steel sheets of Examples A1 to A8.

Table 1. (wt.%, balance is Fe and other inevitable impurities other than P and S)

Serial number	C	Si	Mn	P	S	Cr	Ni	Mo	Cu	Al	Nb	Ti	N	B	Ca	Ca/S	Ceq*
A1	0.04	0.11	0.62	0.010	0.0023	0.21	0.11	0.23	0.10	0.020	0.015	0.010	0.0017	0	0.0035	1.5	0.25
A2	0.05	0.18	0.76	0.99	0.0015	0.02	0.21	0.30	0.12	0.025	0.011	0.030	0.0035	0	0.0020	1.3	0.26
A3	0.05	0.20	1.38	0.010	0.0021	0.11	0.26	0.31	0.001	0.011	0.058	0.012	0.0021	0	0.0027	1.3	0.38
A4	0.06	0.24	1.45	0.010	0.0019	0.28	0.40	0.03	0.34	0.059	0.011	0.013	0.0026	0	0.0024	1.3	0.41
A5	0.08	0.21	1.89	0.99	0.0020	0.32	0.52	0.33	0.48	0.012	0.011	0.059	0.0036	0.0010	0.0026	1.3	0.59
A6	0.10	0.25	1.56	0.008	0.0017	0.31	0.56	0.31	0.21	0.037	0.020	0.015	0.0022	0.0012	0.0020	1.2	0.54
A7	0.11	0.29	1.75	0.012	0.0024	0.34	0.68	0.35	0.15	0.039	0.031	0.018	0.0025	0.0015	0.0043	1.8	0.60
A8	0.12	0.23	1.62	0.011	0.0022	0.39	0.70	0.39	0.17	0.045	0.024	0.020	0.0024	0.0024	0.0025	1.1	0.60

*Note: Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15.

Table 2 lists the process parameters of the method for producing the steel sheets in Examples A1 to A8.

Table 2.

*Note: 1) Slab reheating temperature T=1120+420CNb+190CTi±20; 2) Open rolling temperature is Ar3+200°C～Ar3+350°C, 3) Finish rolling temperature is Ar3+40°C～Ar3+100 °C, 4) The cooling temperature T _n is Ar3 + 15 ° C to Ar 3 + 50 ° C.

Table 3 lists the relationship and average effective grain size parameters satisfied by the relevant chemical elements in the steel sheets of Examples A1 - A8.

table 3.

*Note: d=10-Ceq-d _A /20-2R-(Tn-Ar3)/70-(Tn-T _E )/500-CR/20-F _A /5, where F _A is acicular iron The comparison of the body.

The finished board in the above embodiment is subjected to rod stretching (Ф10 mm) or plate stretching, Charpy V-notch impact, and NDTT performance test (Nil-Ductility Transition Temperature, NDTT performance is an important index for measuring the crack arrestability of the steel sheet) The mechanical properties obtained are shown in Table 4.

Table 4 lists the mechanical properties of the steel sheets having high crack arresting properties in Examples A1 to A8 of the present invention.

Table 4.

Serial number	Yield strength (MPa)	Tensile strength (MPa)	Total elongation (%)	Mean value of impact energy, J (-40 ° C, longitudinal)	NDTT*(°C)
A1	532	627	twenty four	276	-90
A2	507	598	25	287	-95
A3	465	573	25	296	-85
A4	497	584	26	294	-90
A5	446	563	twenty four	304	-85
A6	431	550	33	353	-80
A7	412	524	26	321	-80
A8	425	530	29	340	-75

*Note: NDTT is Nil-Ductility Transition Temperature.

It can be seen from Table 4 that the steel sheets in the examples A1-A8 of the present case have high strength, the yield strength is ≥ 412 MPa, the tensile strength is ≥ 524 MPa, and the low temperature toughness is good, and the average value of the impact work is 276 J or more. The elongation rate is over 24%. Meanwhile, the steel sheets in Examples A1 to A8 also had excellent crack arresting properties, and their plastic-free transition temperatures (NDTT) ≤ -75 °C. Therefore, the steel plate with high crack arresting property according to the present invention can be applied to key parts such as ships and offshore engineering structures. Manufacturing and production of components.

It is to be noted that the above is only specific embodiments of the present invention, and it is obvious that the present invention is not limited to the above embodiments, and there are many similar variations. All modifications that are directly derived or associated by those of ordinary skill in the art are intended to be within the scope of the invention.

Claims (15)

1. A steel sheet having high crack arresting property, characterized in that the chemical element mass percentage content is:

   0.04%≤C≤0.12%,0.10%≤Si≤0.30%,0.60%≤Mn≤1.90%, P≤0.015%, S≤0.0040%,0.01%≤Cr≤0.40%,0.10%≤Ni≤0.70%, 0.001%≤Mo≤0.40%,0.001%≤Cu≤0.50%,0.01%≤Al≤0.06%,0.01%≤Nb≤0.06%, 0.01%≤Ti≤0.06%, N≤0.007%, 0.0001%≤Ca≤ 0.0045%, and 1.0 ≤ Ca / S ≤ 2.0, the balance is Fe and other unavoidable impurities.
2. The steel sheet having high crack arresting property according to claim 1, wherein the steel sheet has an average effective crystal grain size d ≤ 7 μm and a grain orientation difference of ≥ 15°.
3. A steel sheet having high crack arresting property according to claim 2, wherein said average effective grain size d = 10 - Ceq - d _A / 20 - 2R - (Tn - Ar3) / 70 - (Tn - T _E )/500-CR/20-F _A /5; wherein Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15, the unit is wt.%; d _A Indicates the original austenite grain size in μm; R represents the cumulative reduction ratio during rolling, in %; Tn represents the open cooling temperature in °C; Ar3 represents the initial phase transition of steel during slow cooling Temperature, in °C; T _E represents the final cooling temperature in °C; CR represents the cooling rate in °C/s; F _A represents the comparative example of acicular ferrite.
4. The steel sheet having high crack arresting property according to any one of claims 1 to 3, which further contains 0 &lt; B ≤ 0.0025 wt%.
5. The steel sheet having high crack arresting property according to any one of claims 1 to 3, which further satisfies: 0.10 wt% ≤ C + Mn / 6 ≤ 0.50 wt%.
6. The steel sheet having high crack arresting property according to any one of claims 1 to 3, which further satisfies: 0.9 wt% ≤ (Cr + Mo + B) / (C + Mn / 6) ≤ 3.3 wt %.
7. The steel sheet having high crack arresting property according to any one of claims 1 to 3, which further satisfies: 0.9 wt% ≤ (Ni + Nb + Ti + Al) / (C + Mn / 6) ≤ 2.2 wt%.
8. The steel sheet having high crack arresting property according to any one of claims 1 to 3, wherein the microstructure is acicular ferrite + polygonal ferrite.
9. The steel sheet having high crack arresting property according to claim 8, wherein the acicular ferrite is ≥90%.
10. A method for producing a steel sheet having high crack arresting property according to any one of claims 1 to 3, comprising the steps of: smelting, refining, casting, slab heating, controlled rolling, and control cool down.
11. The method for producing a steel sheet having high crack arresting property according to claim 10, wherein in the controlled rolling step, reheating is performed before the rolling, and the heating temperature T is =1120 + 420 C _Nb. +190C _Ti ±20, wherein the temperature unit is °C, C _Nb is the content of Nb, the unit is wt.%, and C _Ti is the content of Ti, and the unit is wt.%.
12. The method for producing a steel sheet having high crack arresting property according to claim 10, wherein in the controlled rolling step, the rolling temperature is Ar3 + 200 ° C to Ar 3 + 350 ° C, and the finishing rolling temperature is Ar 3 +40 ° C ~ Ar3 + 100 ° C.
13. The method for producing a steel sheet having high crack arresting property according to claim 10, wherein in the controlled rolling step, the cumulative reduction ratio is 60 to 99%.
14. The method for producing a steel sheet having high crack arresting property according to claim 10, wherein in the controlled cooling step, the cooling temperature is Ar3 + 15 ° C to Ar 3 + 50 ° C, and the final cooling temperature is 250 ° 450 ° C.
15. The method for producing a steel sheet having high crack arresting property according to claim 10, wherein in the controlled cooling step, the cooling rate is 10 to 30 ° C/s.